This question was sent to a discussion list via email. My reply follows.

Sometimes, I have seen a behavior where the Principal was unable to connect to the Mirror. What is the reason for this behavior? Could it be network? I could not find any information that explain this behavior.

Any help here would be appreciated.

My answer:

This does not mean that the principal is disconnected from the mirror.

This simply means that the Database Mirroring Monitor has not connected to the mirror yet. This is not an unusual behavior to see when first looking at a mirrored database in the monitor. The monitor connects to the principal and then to the mirror. Usually, this will clear up within a few seconds on its own as it eventually makes the connection.

If it does not make the connection on its own within a short time, then the problem exists between the monitor and the mirror.